Arthrocentesis: A procedure in which a sterile needle and syringe are used to drain fluid from the joint. This is usually done as an office procedure or at the bedside in the hospital. For certain conditions, medication is put into the joint after fluid removal. The needle is then removed, and a bandage or dressing is applied over the entry point. Joint fluid can be examined to determine the cause of the joint swelling, such as infection, gout, or rheumatoid disease. Arthrocentesis can be helpful in relieving joint swelling and pain. Also known as joint aspiration.